Photographic silver halide developing solutions containing calcium precipitation inhibitors



Patented Feb. 13, 1951 PHOTOGRAPHIC SILVER HALIDE DEVELOP- IN GSOLUTIONS CONTAINING CALCIUM PRECIPITATION INHIBITORS Richard W. Hennand John I. Crabtree, Rochester, N. Y., assignors to Eastman KodakCompany, Rochester, N. Y., a corporation of New Jersey No Drawing.Application May 28, 1947, Serial No. 751,122

7 Claims.

This invention relates to photography and particularly to methods andmaterials for preventing precipitation of calcium or other insolublesalts in photographic developers and other solutions.

This application is a continuation-in-part of application Serial No.551,780, filed August 29, 1944, now abandoned, which is acontinuationin-part of application Serial No. 508,984, filed November 4,1943, now abandoned.

The precipitation of insoluble calcium salts in water is a problem inmany industries and is particularly objectionable in the photographicindustry because of its efiect on the quality of photographic films andthe usability of photographic processing solutions. The use of certaincomplex phosphates, especially polymerized sodium metaphosphate andsodium or potassium pyro phosphates, in photographic developers toreduce the formation of calcium sulfite scum on the films and calciumprecipitates in the developer is known. Upon standing in aqueoussolutions in the absence of a polyhydroxy carboxylic acid, all of thesephosphates gradually hydrolyze to the orthophosphates (Na3PO4, NazI-IPO4or NaH2PO4, depending upon the pH) which not only possess no inhibitingproperties but may also precipitate the calcium themselves as theflocculent calcium orthophosphates. In addition to this difficulty, theaddition of an excess of these inhibitors to alum fixing baths as whencarried over from the developer, causes the precipitation of aluminumphosphate.

If the metaphosphate and pyrophosphate are expressed in terms of theratio of sodium oxide to phosphorus pentoxide, it will be seen thatsodium metaphosphate has the formula N azO-PzOs and sodiumpyrophosphate-has the formula 2Na2O-P2O5 It is, therefore, an object ofthe present invention to provide a method for preventing precipitationof insoluble calcium salts in water. A further object is to provide amethod for preventing the precipitation of calcium and the formation ofa calcium sulfite scum on photographic films when treated in adeveloping bath. Other objects will appear from the followingdescription of our invention.

These objects are accomplished by using as a calcium precipitationinhibitor an alkali metal phosphate together with a polyhydroxycarboxylic acid or, in certain cases, by using an alkali metalpolyphosphate alone. Our invention includes developers containing suchcompounds, both in' the wet and the dry form.

By polyphosphatetwe mean a compound of the general formula $1VI2O-yP2O5,where M20 represents an alkali metal oxide such as sodium, potassium orammonium oxide, and the ratio of a: t y is greater than 1 but less than2. These compounds fall in a class also known as molecularly dehydratedphosphates (Schwartz and Munter, Ind. & Eng. Chem., 34, 32; 1942).

Examples of the polyphosphates which we propose to use are sodiumtetraphosphate,

3N azO 2P205 sodium tripolyphosphate, 5Na2O-3P2O'5; and a compoundhaving the formula 6NazO-5Pz0s. These compounds have the advantage oversodium metaphosphate (Na2O-P2O5) and sodium pyrophosphate (2NazO-P2O5)of (1) more nearly equal sequestering power for calcium andmagnesiumifor example, metaphosphates are weakly sequestering formagnesium while pyrophosphates are relatively Weakly sequestering forcalcium) (2) less change in pH on hydrolysis in mildly alkalinedevelopers, and (3) in some cases, have superior keeping properties.

Carboxylic acids, more particularly polyhydroxy carboxylic acids, formcomplexes with calcium salts which delay the precipitation of thecalcium. These acids or their salts, when added to the developer insufficient quantity, will delay the formation of the calcium sludgenormally formed whencalcium is added as an impurity in the water or fromthe film. On standing for any considerable period of time, however, thistype of complex decomposes, freeing the calcium for precipitation bysulfite, carbonate, etc.

The principal novelty of the present invention lies in the employment ofa complex alkali-metal phosphate, for example, an alkali-metal salt ofmetaphosphoric acid, pyrophosphoric acid or tetraphosphoric acid inconjunction with a polyhydroxycarboxylic acid or an alkali-metal salt ofsuch acid in order to prevent the precipitation of calcium in analkaline solution containing calcium salts or other salts which aresubject to precipitation in insoluble form. Our invention also includesthe discovery of the superior value.

of sodium tetraphosphate or other polyphosphate as a calciumprecipitation inhibitor when compared with previously known inhibitorssuch as sodium hexametaphosphate or sodium pyrophosphate.

Sodium hexametaphosphate (NaPOs)e and po- 3 tassium pyrophosphate(K4P2Ov) have previously been used in photographic developers. Sodiumtetraphosphate (Na6P4O'13) has not previously been used in developersand possesses advantages over both the hexametaphosphate and thepyrophosphate as pointed out below. Any of the water-solublealkali-metal salts of these com pounds may be used such as the sodium orpotassium salts.

We have found that the inhibiting value of all 10 Of these phosphates isimproved by usin them 'in conjunction with a polyhydroxy carboxylic acidsuch as tartaric, gluconic, mucic, ascorbic saccharic or gallic. Thealkali-metal salts of these acids may also be employed.

Efiective concentrations of the polyhydro-Xy carboxylic acids range from0.5 to 200 grams per' liter of solution and are employed with phosphateconcentrations of from 0.2 to grams per liter. the composition of thedeveloper; for example, low pI-I developers, such as the following.

The most useful quantity will vary with 20 4 and 20 grams of gluconicacid are added, no pre-' cipitate will occur on keeping the resultingsolution for a period of minutes at 100 C.

The use of these inhibitors need notbe confined to the developer but maybe extended to other baths where an insoluble calcium precipitate,aluminum precipitate or precipitate of other polyvalent metal occurs.For example, certain wetting agents used for drying film precipitatewith hard water or with aluminum contaminant from the fixing bath. Smallquantities of a combination of phosphate and polyhydroxy carboxylic acideffectively inhibit this precipitation.

The improved properties of salts of tetraphos- 15 phoric acid, whencompared with those of pyrophosphoric acid or metaphosphoric acid areapparent from the following table. As shown therein, the calciumprecipitation inhibiting bath of the various salts was measured in thedeveloper of Example 7 (without the tetraphosphate) diluted one part ofstock solution to two parts of distilled Water.

Calcium Precipita- Salt Tested Stability Towards Hydrolysis (Min. ofBoiling Solution of Developer of Ex. 7 (1:2) Containing 2 Grams perLiter of Phosphate +0.15 Gram per liter of Calcium Chloride) tionInhibiting Power (Grams per Liter of Calcium Chloride to CausePrecipitate; 2 Grams per Liter of Phosphate in Developer of Ex. 7 (1:2)

Precipitation with Alum (Grams per Liter of Potassium Alum toPrecipitate 1% Phosphate Solutron) 1. Sodium I lexametaphosphatauu 0.6 45 2. Potassium pyrophosphate. 0.4 2 3 3. Sodium Tetraphosphate 0.75 7 l04. None 0.15

I Our invention will be further illustrated by refMonomethyl-p-aminophenol sulfate g 2 erence to the followmg faxamples:Hydroquinone g 5 EXAMPLE 1 g gj Sulfite "f "7g" To a developer of thefollowing composition: Water EJI::::::::::: iit r: 1 -p-a p 1 willrequire smaller quantities than alkaline car-" sulfatef 2 b d 1 h th f uHydroqumone do 5 8 eve operssuc as e 0 Sodium sulfite (anhydrous) do 100II Borax do 2 Monomethyl-p-aminophenol sulfate g 2.2 Water 'T fI-Iydroquinone g 8.8 t ere were added 0.5 gram of sodiumhexa'metasodiumsdmte, desiccated g 96 phosphatear d 2 gramsof'gluconic'acid. These" Sodium carbonate, desiccated; g 48 5Q fi l thed veloper against 0.7 gram of Calcium Potassium br0mide g 5 chlorideduring a storage period of 6 weeks at Water to liter 1 If one gram ofcalcium chloride is added to one liter of developer I, an immediateprecipitation of calcium sulfite occurs. If 2.5 grams of sodiumtetraphosphate are present per liter of developer, no immediateprecipitate occurs but one will appear when this solution is held at C.for approximately 2 /2- minutes. If 20 grams of gluconic acid are addedper liter in place of the tetraphosphate and the solution held at 100C., a precipitate will appear in about minute. If both the 2.5 grams oftetraphosphate" 76 No precipitatio EXAMPLE 2 To the developer formula ofExample 1, 2.5 grams of sodium tetraphosphate and 10 grams-o sodium saltof mucio' acid are a'dded. These protect the developer againstprecipitationby one gram of calcium chloride which would cause a denseprecipitate if they were not present. On

boiling, this combination was stable for 4 times" To developer II, 2.5grams of sodium tetraphosphate and 20' grams of gallic' acid were addedand then 0.7 gram of calcium chloride was added;

Ii Ocdtlrrd' and, on'bollin'g, this" solution was stable for 20 timesthe period of the same solution containing sodium tetraphosphate andcalcium chloride but no gallic acid.

EXAMPLE The followin solution is used for drying film, using hard water(5 A grains per gallon temporary hardness) Water oc 500 Sodiumtetraphosphate gram 0.2 Sodium gluconate do 0.5 Dioctyl ester of sodiumvsulfosuccinic acid solution in ethyl alcohol) cc 10 Water to liter 1 Inthe absence of the precipitation inhibitors, the dioctyl ester of sodiumsulfosuccinic acid yields only a very cloudy solution. Even whenprepared with distilled water, it soon precipitates as it iscontaminated with the wash water and with traces of aluminum carriedthrough from the fixing bath. In the presence of the inhibitors thesolution is entirely clear and remains so throughout a normal exhaustionlife.

EXAMPLEG To the developer of Example 1 there was added 0.5 gram ofsodium tetraphosphate. This developer was found to tolerate the additionof over 2 grams of anhydrous calcium chloride or its equivalent perliter without allowing the formation of a precipitate and also was foundto prevent the formation of calcium sulfite scum on films even after 4weeks storage at 75 F.

EXAMPLE 7 To the following formula Monomethyl-p-aminophenol sulfategrams 3.1 Hydroquinone do 12 Sodium sulfite (anhydrous) do 45 Sodiumcarbonate (anhydrous) do 67.5 Potassium bromide do 1.9 Water to liter 1there was added 6 grams of sodium tetraphosphate. This developer, whendiluted one part with 2 parts of water, did not produce pronouncedsludge even after development of '70 8 x 10 inch sheets of photographicpaper while the corresponding formula without the employment of thetetraphosphate produced sludge.

EXAMPLE 8 These chemicals are sufiicient to make 1 liter of developerwhen added to water. The tetraphosphate is incorporated in the packagein order to produce a clear solution upon mixing with hard water.

EXAMPLE 9 CompartmentA Grams Monomethyl-p-aminophenol sulfate 4.0

Compartment B Grams Sodium sulfite (anhydrous) 45.0 Sodium carbonate(anhydrous) 67.5 Potassium bromide 1.9 Sodium tetraphosphate 6.0 Sodiumgluconate 24.0

These chemicals are sufficient to make 1 liter of stock solution. Thepresence of the sodium tetraphosphate insures a clear solution on mixingwith hard water, while the sodium gluconate decreases the rate ofhydrolysis of the tetraphosphate while standing in solution.

EXAMPLE 10 In any of the above solid mixtures containing alkali-metalpolyphosphates the tendency of the polyphosphate to fuse or become tackyon exposure to moist air may be overcome by mixing an inert alkali-metalsulfate, such as anhydrous sodium or potassium sulfate, with thepolyphosphate. A mixture of one part of sodium tetraphosphate with twoparts of anhydrous sodium sulfate or potassium sulfate was found toremain free flowing upon an exposure to an atmosphere of 70% relativehumidity for two weeks, the concentration may vary from one part ofpolyphosphate in from to 20 parts of alkali-metal sulfate.

EXAMPLE 11 The presence of iron in some polyphosphates may causeincreased development fog. This fog may be controlled by the addition ofantifoggants such as a1kali-metal bromides and iodides, or organicantifoggants such as 1, 2, 3-benzotriazole and o-nitrobenzimidazole. Asample of sodium hexametaphosphate containing 0.03% of iron was found togive bad fog when added to developing solutions for high speed negativeemulsions. The presence of 0.05 gram of 1,2,3-benzotriazole per gram ofsodium hexametaphosphate prevented this fog.

The concentration of antifoggant may vary from 1 part of antifoggant tofrom 2 to 200 parts of phosphate in the case of potassium iodide, 1,2,3-benzotriazole and fi-nitrobenzimidazole nitrate and from 1 part ofantifoggant to from 0.1 to 10 parts of phosphate in the case ofpotassium bromide.

EXAMPLE 12 To the formula of Example 7, diluted 1 part to 2 parts ofwater (without the tetraphosphate) there was added 2 grams per liter ofsodium tripolyphosphate (NasPsOio). This prevented precipitation ofcalcium when present at a concentration of 500 parts per million(expressed as CaClz) EXAMPLE 13 To Formula I there was added 0.5 gramper liter of sodium tripolyphosphate. This prevented precipitation ofcalcium when present at concentration of over 1000 parts per million(expressed as CaClz).

EXAMPLE 14 Na12P1uO31(6Na2O.5PzO5) when used to replace sodiumtripolyphosphate in Examples 12 and 13, was found to functionsuccessfully as a calcium sequestering agent.

It will be understood that the examples included herein are illustrativeonly and that our in vention is to be taken as limited only by the scopeof the appended claims.

We claim:

1. An alkaline photographic developing solutio'n comprising asilverhalide developing agent, from 0,2 to 20 grams per liter of solution ofan alkali-metal phosphate having the formula alkaline material, and from0.5 to 200 grams per liter of solution of a polyhydroxy carboxylic acid.

3. An alkaline photographic developing solutioncomprising a silverhalide developing agent an alkaline material, and from 0.2 to 20 gramsper liter of solution of sodium tetraphosphate.

4. A photographic developer in dry form comprising a silver halidedeveloping agent, sufiicient alkali-metal phosphate having the formula.rMzO 111 205 where M is an alkali metal, and r and y represent numbersin which the ratio of a: to y is greater than 1 but less than 2, toproduce 0.2 to 20 grams per liter in solution, a sufficient amount of acompound selected from the class consisting of polyhydroxy carboxylicacids and their alkali-metal salts to produce 0.5 to 200 grams per literin solution, and sufficient alkaline material to produce an alkalinedeveloping solution.

5. A photographic developer in dry form comprising a silver halidedeveloping agent, suificient alkali-metal salt of tetraphosphoric acidto produce 0,2 to 20 grams per liter in solution, a sufficient amount ofa compound selected from the class consisting of polyhydroxy carboxylicacids and their alkali-metal salts to produce 0.5 to 290 grams per literin solution, and suficient alkaline material to produce an alkalinedeveloping solution.

6. A photographic developer in dry form comprising a silver halidedevelo'ping agent and sufficient alkali-metal "salt of tetraphosphoricacid to produce 02-170 20 grams per liter in solution, and sufficientalkaline material to produce an alkaline developing solution.

7. A dry powder composition for the preparationof photographicdeveloping solutions by adding to water, comprising a silver halidedeveloping agent, sufiicient alkali-metal tetraphosphate to produce 02to 20 grams per liter in solution and a sufficient amount of a compoundselected from the class consisting of po-lyhydroxy carboxylic acids andthe alkali-metal salts of said acids to produce 0.5 to 200 grams perliter in solution, and sufilcient alkaline material to produce analkaline developing solution when the mixture is dissolved in water.

RICHARD W. HENN. JOHN I. CRABTREE.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,424,062 Agnew et a1 July 25,1922 2,019,665 Fiske et a1. Nov. 5, 1935 2,086,867 Hall July 13, 19372,091,689 Russell Aug. 31, 1937 2,092,913 Fiske 'Sept. 14, 19372,145,827 Chester Jan. 31, 1939 2,168,181 Ulrich et a1. Aug. 1, 19392,172,216 Miller Sept. 5, 1939 2,214,216 Webster Sept, 10, 19402,238,547 Wood Apr. 15, 1941 2,239,284 Draisbach Apr. 22, 1941 2,257,440Wood Sept. 30, 1941 FOREIGN PATENTS Number Country Date 171,922 GreatBritain Sept. 13, 1937 1 OTHER REFERENCES Washing, Cleaning andPolishing Materials, Bureau of Standards Circular C424 (1939), page 28.

1. AN ALKALINE PHOTOGRAPHIC DEVELOPING SOLUTION COMPRISING A SILVERHALIDE DEVELOPING AGENT, FROM 0.2 TO 20 GRAMS PER LITER OF SOLUTION OFAN ALKALI-METAL PHOSPHATE HAVING THE FORMULA